The present invention generally relates to communication devices, and in particular to radio devices receiving simultaneously speech and data.
Communication devices (transmitter and/or receiver) are usually designed either as devices for speech transmission (xe2x80x9cspeech devicesxe2x80x9d, e.g. telephones) or as devices for data transmission (xe2x80x9cdata devicesxe2x80x9d, e.g. selective pager). The term xe2x80x9cspeechxe2x80x9d is used in this description as a representation for all information (speech, music, morse code, and the like) which can be transmitted acoustically in the audible frequency range (e.g. 16 Hz to 16 kHz, dependent on the person) to a user. The term xe2x80x9cdataxe2x80x9d will be used in this description for all other information. However, the usual differentiation in speech devices and data devices does not exclude that speech devices should as well transmit data in a certain smaller extent (e.g. short messages in mobile telephones) and data devices should transmit as well speech (e.g. telephone communication via data networks).
Therefore, there is a need for combined speech and data devices. Such devices are realized according to the prior art as follows:
speech and data can be transmitted sequentially (time multiplex) via one transmission channel. For instance an analogue telephone line or a radio channel transmits either speech or data but not both, speech and data, at the same time. The speech communication is excluded at the time of a data transmission and vice versa. Noises which usually occur with the coding of data in the channel in the audible range (xe2x80x9cmodem noisexe2x80x9d) are perceived as disturbing by the user.
speech and data can be transmitted essentially simultaneously by means of extensive digital coding at the transmitter side and similarly extensive decoding at the receiver side. Examples are telephone systems according to the ISDN standard (Integrated Service Digital Network) or digital mobile radio telephones (e.g. GSM standard).
FM broadcast transmitters code data (e.g. weather messages, traffic messages) on subcarriers transmitted parallel to the main broadcast program (speech). Large decoders are necessary at the receiver side. Additionally, the communication is possible in one direction only.
Means for analogue radio devices are known under the names xe2x80x9cprivate linexe2x80x9d (PL) and xe2x80x9cdigital private linexe2x80x9d (DPL), by means of which the transmitter adds a pilot sound detected and evaluated at the receiver side, wherein the speaker at the receiver side can be switched selectively on and off. Such means have a protection function and avoid the transmission of speech to persons who do not want to listen or who should not hear the corresponding speech. A useful documentation is the following handbook: xe2x80x9cMotorola Inc, Schaumburg, Ill., xe2x80x98Digital Private-Linexe2x80x99, Binary-Coded Squelch, Theory and Servicing Fundamentals, Reference Manual 68P81106E83-A, 1975xe2x80x9d.
There is a need to provide an improved communication device for simultaneous transmission of speech and data.